Alzheimer's disease (AD) is the major cause of dementia in the elderly, affecting approximately 3-4 million people in the United States alone. The decline of cognitive abilities in AD is associated with pathologic changes in the brain, the most prevalent of which are the formation of amyloid plaques and neurofibrilary tangles (Selkoe, Physiol. Rev. 81:741-766, 2001). Amyloid plaques in AD brains form at far greater numbers than in normal individuals. While amyloid plaques contain many proteins, they have as their principal constituent the 4 kDa amyloid-β (Aβ) peptide (Kang et al., Nature 325:733-736. 1987). The formation of the Aβ peptide, and thereby Aβ amyloid, arises from aberrant processing of the amyloid precursor protein (APP). A number of studies support the idea that Aβ is itself neurotoxic, and therefore the high concentration of Aβ peptide in amyloid plaques may seed the generalized degeneration of neurons in surrounding areas (Morris and Price, J. Mol. Neurosci. 17:101-118, 2001).
One approach to inhibiting AD would appear to be to inhibit the proteases, in particular the K- and β-secretase, that produce the Aβ peptide. However, individuals without AD also have plaques, and as some Aβ peptide is produced in people without AD. Therefore, such peptide processing may be a byproduct of necessary protease functions and inhibiting APP processing may have unwanted and toxic consequences.
Another approach would be to design therapies that would either eliminate the toxic aspects of amyloid plaques or remove plaques from the brain altogether. For example, Aβ toxicity is associated with the generation of reactive oxygen species (Parks et al., J. Neurochem. 76:1050-1060, 2001) and with the accumulation of heavy metals (Cherny et al., Neuron 30:665-676, 2001). Therefore, the creation of a reducing or chelating environment locally at amyloid plaques may inhibit the toxicity associated with Aβ in these areas. Because many proteins in addition to Aβ accumulate in amyloid plaques, the activation of proteases may also aid in plaque removal or lessen plaque number or plaque size. Blocking of the cellular receptors that mediate Aβ toxicity in neurons may also have a therapeutic benefit.
These approaches would be greatly facilitated by the ability to target therapeutics directly to amyloid plaques. One way to do this would be to develop reagents that specifically bind Aβ amyloid and can be conjugated with therapeutic or diagnostic molecules. It is an object herein, among other objects, to provide reagents that specifically react with Aβ amyloid, diagnostic assays using such reagents, and methods for preparing reagents for identifying disease causing forms of other amyloid proteins and other disease-associated conformation dependent proteins.